It has been the usual practice that, in an outboard engine, the ignition timing during trolling is set in the vicinity of 0.degree. to 10.degree. of crankshaft angle after the top dead center or top dead point in view of the necessity for maintaining smooth revolution of the engine at a very low speed. In this case, as the number of revolutions of the engine and the speed of the marine vessel are preferably as low as possible during trolling, the ignition timing is set as late as possible. Because of the foregoing reason, the throttle opening degree is closed as much as possible. Generally speaking, the ignition timing is spark advanced as the engine speed is increased or as the throttle opening degree is increased.
In general, marine vessels have a large traveling resistance. Owing to the foregoing, when a shift is made to the forward position or reverse position after the engine has been started, a large load is suddenly applied to the engine, thus easily resulting in stalling of the engine.
To the contrary, when the throttle is suddenly returned to neutral during traveling for the purpose of coming alongside a pier, the number of revolutions of the engine is rapidly reduced. In this case, the supply of air-fuel mixture generally becomes unstable and this also frequently results in stalling of the engine.
If such stalling of an engine occurred when the marine vessel was about to come alongside the pier or when the marine vessel was about to pass another marine vessel traveling in the opposite direction, danger would be encountered.
In order to prevent this kind of stalling of an engine, it is possible to set the number of revolutions of the engine to a somewhat higher level. In such a case, however, there was an inconvenience in that the required low speed traveling during trolling was disturbed because the minimum speed of the engine became too fast.
One object of the invention is, for the purpose of obviating the above inconvenience inherent in the prior art, to provide a method for controlling the ignition timing of an engine for a marine vessel which is capable of smoothly controlling the revolution of the engine without giving rise to stalling of the engine due to sudden change in a load, particularly during low speed traveling.